Field of the Invention
The invention relates generally to electric motor construction, and more particularly to motors in which a tapered bearing sleeve is used to centralize a rotor with respect to the axis of rotation of a rotor bearing assembly and motor shaft.
Related Art
Oil and natural gas are often produced by drilling wells into oil reservoirs and then pumping the oil and gas out of the reservoirs through the wells. If there is insufficient pressure in the well to force these fluids out of the well, it may be necessary to use an artificial lift system in order to extract the fluids from the reservoirs. A typical artificial lift system employs an electric submersible pump (ESP) which is positioned in a producing zone of the well to pump the fluids out of the well.
An ESP system includes a pump and a motor which is coupled to the pump and drives the pump. The ESP system may also include seals, gauge packages and other components. Because they are designed to fit within the borehole of a well, ESP systems are typically less than ten inches wide, but may be tens of meters long. The motor of an ESP system may produce hundreds of horsepower.
The motor of the ESP system is typically an AC induction motor. The motor has a stator that is cylindrical with a coaxial bore. A cylindrical rotor is coaxially positioned within the bore of the stator. The rotor is coupled to a shaft so that rotation of the rotor turns the shaft. Rotor bearing assemblies hold the rotor in position within the bore of the stator and allow the rotor to rotate smoothly within the bore.
Conventionally, the rotor has a coaxial bore which extends through it. The rotor is installed on the shaft so that the shaft extends through the bore. There is normally a gap between the rotor and the shaft. This gap allows the rotor to move axially on the shaft. This is necessary to allow the rotor to be installed on the shaft, and to allow the rotor to move on the shaft as the motor expands and contracts with changes in temperature.
While the gap is necessary for the construction and proper operation of the motor, it can also cause some problems. More specifically, the gap may allow the rotor to move laterally (perpendicular to the axis of the motor. Consequently, the rotor may not rotate smoothly with respect to the axis of rotation, but may instead orbit the axis. In other words, the axis of the rotor may be offset from the axis of rotation. This may cause vibration and excessive wear that may shorten the life of the motor.
It would therefore be desirable to provide means to maintain the coaxial positioning of the rotor with respect to the rotor bearing assemblies and the axis of rotation, thereby reducing vibrations in the motor.